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Appl. Environ. Microbiol. doi:10.1128/AEM.02945-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Phylogeography of the thermophilic cyanobacterium Mastigocladus cf. laminosus

Division of Biological Sciences, The University of Montana, Missoula, MT 59812

^* To whom correspondence should be addressed. Email: scott.miller{at}mso.umt.edu.

	Abstract

We have taken a phylogeographic approach to investigate the demographic and evolutionary processes that have shaped the geographic patterns of genetic diversity for a sample of isolates of the cosmopolitan thermophilic cyanobacterium, Mastigocladus cf. laminosus, collected from throughout most of its range. Although M. laminosus is found in thermal areas throughout the world, our observation that populations are typically genetically differentiated on local geographic scales suggests the existence of dispersal barriers, a conclusion corroborated by evidence for genetic isolation by distance. Genealogies inferred using nitrogen metabolism gene sequence data suggest that a significant amount of the extant global diversity of M. laminosus can be traced back to a common ancestor associated with the western North American hotspot currently located below Yellowstone National Park. Estimated intragenic recombination rates are comparable to those of pathogenic bacteria known for their capacity to exchange DNA, indicating that genetic exchange has played an important role for generating novel variation during M. laminosus diversification. Selection has constrained protein change at loci involved in the assimilation of both dinitrogen and nitrate, suggesting the historic use of both nitrogen sources in this heterocystous cyanobacterium. Lineage-specific differences in thermal performance were also observed.

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